Read back through the thread Daffodil
There are several posts explaining clearly why it's worth waiting until September. Then we reassess.
Possibly it won't be safe even then (we can't plan very far in advance during a pandemic) but it buys us more time. Time for more research.
Experts are learning new things everyday about the virus. The Covid toe issue and the ill children with rashes has only recently become apparent. We might know a bit more about possible long-term effects by then. We might not, but we certainly have more chance than if we recklessly rush a return to schools and work (with the inevitable second wave and second lockdown that would follow).
As well as work progressing on vaccines, we're seeing promising results with the drugs trials. So far they seem fairly effective if given early.
And very simply. Longer lockdown leaves the virus with nowhere to go. There's only so many people it can infect during a lockdown. Then again ours won't work unless and until we stop unessential flights (or implement checks and quarantine).